Thermal storage systems have been in existence for many years. The purpose of a thermal storage system is to create thermal energy and store it for use at another time. In a typical thermal storage system, the refrigeration system, i.e., a chiller, generates ice at night when electrical utility rates are typically lowest (off-peak). During the day, when utility rates are higher (on-peak), the ice is then melted to provide, for example, cooling to a building.
One type of technology system that provides for thermal storage is referred to as “ice on coils”. In this type of system, cylinders of ice are built onto tubes (coil tubes; also referred to as thermal storage coils). In many systems that use this technology, multiple banks of coils are submerged under water in concrete, metal or resin tanks.
Many thermal storage systems use glycol chillers to provide cooling necessary to generate ice on the coil tubes. Such thermal storage systems have two modes of operation, “ice build” and “ice melt”. For ice build, the glycol chiller is energized during the off-peak period. The glycol chilling system generates low-temperature glycol that circulates through the coil tubes of the thermal storage coils. The circulating glycol removes heat from the water in the tank which causes water to freeze onto the exterior surface of the thermal storage coils. During ice melt, the glycol chilling system is shut off, i.e. de-energized. For one type of “ice melt” phase, the tank water is circulated over the ice built-up on the thermal storage coils to extract energy from the ice. The ice water is then circulated through a primary side of a heat exchanger.
A conventional component of one type of thermal storage system is a thermal storage coil assembly 2 as shown in FIG. 1. The thermal storage coil assembly 2 includes a tank 4 containing tank water (arrows in FIG. 2) and a plurality of thermal storage serpentine circuits 6 with each thermal storage serpentine circuit 6 including a plurality of horizontally-extending, integrally interconnected coil tubes 8.
As shown in FIG. 2, the geometry of the coil tubes 8 is such that ice I may overbuild (overbuilt ice OI) in the vertical direction but a vertically-extending clearance gap G is necessary between rows of horizontally-disposed coil tubes 8. Thus, the vertical clearance gap G between the rows of coil tubes 8 permits circulation of the tank water (illustrated as arrows in FIG. 2). Maintaining the clearance gap G as an open, serpentine, vertical passageway between the ice I building on respective one of the coil tubes 8 allows for efficient heat transfer between the tank water and the ice I on the coil tubes 8 of thermal storage serpentine circuits 6.
It is therefore beneficial to either measure or monitor the amount of ice that accumulates on the coil tubes 8 of the thermal storage serpentine circuits 6 to provide at least some assurance that the vertical clearance gap G is maintained throughout the ice build-up operation phase of the thermal storage system. There are several ways for measuring or monitoring the amount of ice I in the tank 4 of the thermal storage system. One method of measuring ice is by the level of tank water in the tank 4. Another method is to measure or monitor the amount of ice I accumulating on a coil tube 8 of a thermal storage serpentine circuit 6. One type of an ice thickness measuring device senses the thickness of the ice I by conductivity. Another conventional ice thickness measuring device 10, such as the one shown diagrammatically in FIG. 1, is placed on the coil tube 8 of the thermal storage serpentine circuit 6 to measure or monitor levels of the ice thickness to detect stages, i.e., percentages of full ice build, in the ice build cycle. When full ice build is reached, a controller 12 in electrical communication with the conventional ice thickness device 10, for example, by a wire 14, shuts off the glycol flow to the thermal storage coils 6 thereby discontinuing the ice build cycle.
The present invention provides an ice thickness probe, an ice thickness probe assembly and an ice thickness monitoring apparatus that are used to measure and/or monitor ice thickness and/or to shut off the thermal storage system when full ice build is reached.